No redraw after assigning new vertex position with python
If your running the script with the object in edit mode then you can use

# Note that bmesh is the module named bmesh, not an instance of a BMesh.
# me is an instance of Mesh, again, not an instance of a BMesh.
bmesh.update_edit_mesh(me)


If your running in object mode then you need something that will trigger an update, not sure if this is the best way but

bpy.context.scene.objects.active = bpy.context.scene.objects.active


triggers an update in the 3dview.